The Genetic Diversity And Genetic Effects Of IGF-1 Gene In Different Pig Breeds

PCR-SSCP,DNA sequencing and satellite detection technique were applied in this study to analyze the distribution of IGF-1 gene in 8 different pig breeds. Molecular biology and statistic genetics methods were used to predict the conformation changing caused by the mutation. The genetic effects of the three genes polymorphisms were investigated on meat quality and carcass traits in different porcine populations. The main results are as follows:3 mutation sites in exons of the IGF-1 genes were detected: there was a mutation (G→A) at 201 bp of the exon 3 and A→G,T→C mutation at 440,455 bp of the exon 4 of the IGF-1 gene. The alteration of a single base in exons are all silent mutation, no substitution of Amino acid happened. The alteration of a single base in these exons were caused by the swinging of genetic coden. (CA)₁₇,(CA)₁₉ and (CA)₂₁ DNA sequencing repeats are detected in the 5' flank of the microsatellite.Three genotypes (AA, AB, BB) were detected in all porcine populations and the distribution of allele and genotype frequencies differed significantly in different porcine populations at exon3 site. Foreign country pig populations had higher frequency of genotype AA and allele A; genotype BB only could be selected in Zang pig, Ya'nan pig and Dawu pig populations. It had higher frequency of allele A in all pigs. This site had intermediate Polymorphism Information Content (0.25＜PIC＜0.5), PIC=0.3531. Exon4 site, three genotypes (EE, EF, FF) were detected in all porcine populations, and foreign country pig populations had higher frequency of genotype EE. However genotype FF only was detected in Zang pigs and Dawu pigs. All pig populations had higher frequency of allele E except for Dahe pigs. This site had low Polymorphism Information Content (PIC＜0.25), PIC =0.1763.5' flank of the microsatellite site, six genotypes (CC,DD,GG,CD,CG,DG) were detected in all porcine populations. Frequency of allele C,D,G is 0.4405,0.4306 and 0.1289. It is a high Polymorphism site (PIC＞0.5), PIC =0.6028.The results ofχ² showed that Changya pig population was biased very significantly from Hardy-Weinberg equilibrium (P＜0.01), but all the other populations were fit with Hardy-Weinberg equilibrium at these 2 exon sites. The populations were biased significantly from H-W equilibrium at 5' flank of the microsatellite site except for Zang pigs and Dawu pigs.The association analysis found that there was a significant association between the SNP and intramuscular fat(IMF) content and marble score. Some significant conclusions can be made on other meat quality and carcass traits at exon 3 site.The association analysis found that exon4 site influenced meat quality traits at various level (P＜0.05, P＜0.01). It influenced intramuscular fat content significantly (P＜0.01), influenced muscle fiberarea and influenced driploss. The allele F had positive additive effects on meat quality traits.The association analysis found that there was a significant association between the SNP and intramuscular fat content, amino-acid composition, and fat acid composition at 5' flank of the microsatellite site. Some significant conclusions can be made on other meat quality and carcass traits.In concluding, the LSM analysis results showed that genotype AA-FF showed its advantage in meat quality traits, and the combination AA-EE showed its advantage in carcass traits.The results suggested that insulin-like growth factorI(IGF-I) gene is potential genetic markers in the study on porcine muscle growth and could be used as markers in marker assisted selection to improve the eficiency and accuracy of selection.